1. Field of the Invention
This invention relates to manifolds for internal combustion engines.
2. Description of the Prior Art
Conventional manifolds for internal combustion engines comprise a system of internal conduits communicating at one end with a series of apertures in a mounting flange, and at the other end with a common opening in the manifold. The manifolds are usually formed by gravity casting using a metal die and a sand core. The resulting castings generally have a poor surface finish. The mounting flange, therefore, requires machining to provide a flat surface which can be sealed to the internal combustion engine block, and the rough internal surface provides resistance to the flow of gases through the manifold.
Manifolds have been produced by pressure casting which produces a smooth finish on the internal and external surfaces of the casting, so that further machining of the casting is unnecessary and the casting has good flow properties. In a pressure casting process, the manifold cannot normally be produced as a single casting since solid cores are used to form the internal configuration of the manifold. Pressure moulded manifolds are, therefore, produced with two or more body parts which are sealed together after formation. The formation of effective and durable seals between the two components presents a considerable problem, particularly where the manifold includes an internal passages jacket for heat exchange with the gases passing through the manifold.